Routing Table
Dynamic routing protocols are used by layer-3 devices including routers and layer-3 switches to exchange their routing information. Each routing protocol has its rule to exchange the information in the form of messages and use an algorithm to determine the best paths that are put into the routing table.
Here is the main functions of dynamic routing protocols:
- Discovery of remote networks.
- Maintaining up-to-date routing information.
- Choosing the best path to destination networks.
- Ability to find a new best path if the current path is no longer available.
Dynamic routing protocols have the primary components below:
- Data structures: organized in tables or databases which are kept in RAM.
- Routing protocol messages: protocol data unit to discover neighboring routers, exchange routing information, learn and maintain accurate information about the network.
- Algorithm: a finite list of steps used to exchange routing information and determine the best paths to destinations.
Categorization:
| IGP | EGP | ||||
|---|---|---|---|---|---|
| Distance Vector | Link-State | Path Vector | |||
| IPv4 | RIPv2 | EIGRP | OSPFv2 | IS-IS | BPG-4 |
| IPv6 | RIPng | EIGRP for IPv6 | OSPFv3 | IS-IS for IPv6 | MP-BGP |
| No. | Protocol | AD | Algorithm | Published Year | Reference |
|---|---|---|---|---|---|
| 1 | RIPv1 | 120 | Bellman-Ford and Ford–Fulkerson | 1988 | RFC 1058 |
| 2 | RIPv2 | 120 | Bellman-Ford and Ford–Fulkerson | 1994 | RFC 1723 |
| 3 | RIPng | 120 | Bellman-Ford and Ford–Fulkerson | 1997 | RFC 2080 |
| 4 | IGRP | 100 | Bellman-Ford | 1992 | Cisco IGRP |
| 5 | EIGRP |
- Summary: 5 - Internal: 90 - External: 170 |
DUAL | 1993 2016 |
Cisco EIGRP RFC 7868 |
| 6 | EIGRP for IPv6 |
- Summary: 5 - Internal: 90 - External: 170 |
DUAL | 2016 |
RFC 7868 |
| 7 | OSPFv2 | 110 | Dijkstra | 1991 |
RFC 1247 |
| 8 | OSPFv3 | 110 | Dijkstra | 2008 |
RFC 5340 |
| 9 | IS-IS | 115 | Dijkstra | 1990 |
ISO 10589 RFC 1195 |
| 10 | IS-IS for IPv6 | 115 | Dijkstra | 2008 |
RFC 5308 RFC 5120 |
| 11 | BPG-4 |
- Internal: 200 - External: 20 |
Best Path | 2006 | RFC 4271 |
| 12 | BPG-MP |
- Internal: 200 - External: 20 |
Best Path | 2007 | RFC 4760 |
Metrics are quantitative values that routing protocols use determine the overall “cost” of a path from source to destination. If there are multiple paths to the same remote network, routing protocols determine the best path based on the route with the lowest cost. Different routing protocols use different metrics. The metrics used by one routing protocol are not comparable to the metrics used by another routing protocol. Two different routing protocols might choose different paths to the same destination.
The following table shows the metrics used by the dynamic routing protocols
| No. | Protocol | Hop Count | Cost | Bandwidth | Delay | Load | Reliability | MTU | Expense | Error |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | RIPv1 | check | ||||||||
| 2 | RIPv2 | |||||||||
| 3 | RIPng | |||||||||
| 4 | IGRP | check default |
check default |
check | check | check | ||||
| 5 | EIGRP | check default |
check default |
check | check | |||||
| 6 | EIGRP for IPv6 | |||||||||
| 7 | OSPFv2 | check | ||||||||
| 8 | OSPFv3 | |||||||||
| 9 | IS-IS | check default |
check | check | check | |||||
| 10 | IS-IS for IPv6 | |||||||||
| 11 | BPG-4 | BGP does not determine the best paths based on metrics. Instead it uses a collection of path attributes. | ||||||||
| 12 | BGP-MP | |||||||||
IGP: Interior Gateway Protocol
EGP: Exterior Gateway Protocol
RIP: Routing Information Protocol
IGRP: Interior Gateway Routing Protocol
EIGRP: Enhanced Interior Gateway Routing Protocol
OSPF: Open Shortest Path
IS-IS: Intermediate System to Intermediate System
BGP: Border Gateway Protocol
MP-BGP: Multiprotocol Border Gateway Protocol
AD: Administrative Distance
DUAL: Diffusing Update Algorithm
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